Bourdon tube for pressure gauges, liquid expansion thermometers, and other instruments



June 1933- H. w. IBBOTT 1,913,239

BOURDQN TUBE FOR PRESSURE GAUGE LIQUID EXPANSION THERMOMETERS. AND OTHER STRUMENTS Filed May 25, 1931 was W,

reamed June 6, i933 Bourdon tubes for pressure gauges, liquid ex UNITED STAT HAROLD WILLIAM IBnoTrQor? L NDO QENGLAND, nssIGNon T NEGBETLI & ZAMBRA,

a t or LoNDoN, ENGLAND y t :BoU RnoN aeemmmas eta GAUGES, LIQUID EXPANSION Trimmer/[mans AND a o rHnn INSTRUMENTS Application filed May 25, 1931, aria No. 539,957, and in Great Britain March 13, 1931.,

, This invention relates to improvements in pansion thermometers and other instruments.

A Bourdon tube consistsof a flattened tube of metal bent into an arc of a, circle or other curve. When pressure is applied tothe interior of the tube, the flattened walls of the tube defiect,"causing the Bourdon tube to asy y sume-a greater radius of curvature' The Bourdon tube may be in the {form of an are or may consistofmany convolutions forrn-f ing a helix ofone or more turns. If one end of the Bourdon tube be fixed,the free end will deflect when pressureis applied to thevinside- H 5 of the tube, and this deflection is a direct indication of the pressure or of the increase in volume of the space enclosed by the walls of the tube. When a Bourdon tubeis employed to indicate pressure or expansion, its

deflectionmay be magnifiedby linkage and fgearing, or anindex may be directly aflixed i to the free end [of thetube, or any Othersuit able means may beemployed to translate the deflection to an indicating or recording dev ce.

For certain purposes particularly when the Bourdon tubeis applied to distance reading thermometers, it is necessary tojreduce the internalvolume of the Bourdon tube to a minimum, and in thiscase the ,wallsof V t the tube areflattened on themselves, so as to leave only a shallow intervening gap.

i A Bourdon tube formedinthis way isliable to fail by fractureat its edge after anumber of. dilations, owingto the material fa- I tiguing,the strain being concentrated in the vicinity of the edges of the shallow internal 'ap. p b The purpose of this i the life of the Bourdon tube, particularly 7 when it is necessary to formthetubeso that it has little internal volume. r

According to the present inventiongthe construction of the tube is modified ,by reducing iv the thickness of the walls 'ofthe tubefabout those parts of the "shallow internalgap ap preaching towards but before reaching the edges ofthe gap, so that upon dilationlittle if any separation ,of the walls occurs at the edges of the gap, that is to say divergence of invention is to increase the wane starts some distance away from i these edges. In this way splitting strain is removed from the material where the internal proaching towards but before reachingthe edges of the gap. Thislocalizedreduction of thethicknessof the walls is suitably effected by recessing (in a gentle curve) the external surface at the tube.

V The invention will now be further described with reference to the accompanying drawing, the views in which are enlarged transverse sections ofa Bourdon tube. Figure 1 shows a Bourdon tube constructed according tofthe invention, and Figure 2 is an exaggerated view ofthis tube dilated. a

In the usual form of Bourdon tube,the walls are flattened on one another so as to leave little intervening space 3 between them; When internal pressure has dilated such a tube several times it is found that the tube 'willfail by fracture at the edges 4: and 5 of the internal gap, owing to the material fatiguing under the splittingstrain.

Figures 1 and 2 illustrate how this can be prevented according to the present invention. Referring to these figures, it Will be seen that the walls of the tube are reduced in thickness by recessingthe outer surface as at A, B, (l and ,D, thereby increasing the transverse flex- "ibility at these points, so that when pressure is set up internally the dilation will commen ce at A, B, C, D, that is at some distance a "-fromthe edges' l and 5, substantially no (11- vergence taking place at the edges as shown Figure 2. l v What I claimis:- i

Bourdon tube having opposed relatively flat wallsjproviding a shallow internal gap, i,

between them, thesaid-walls having parallel 1 longitudinal grooves adjacent the transverse edges ofthe tube whereby the walls are pro vided'with zones of reduced thickness.

In testimony that I claim the foregoing as my invention I havesigned my name this 7th day of May, 1931.

HAROLD WILLIAM IBBOTT.

CERTIFICATE OF CORRECTION.

Patent No. 1,913,239. June 6, 1933.

HAROLD WILLIAM IBBOTT.

It is hereby certified that the name of the first mentioned assignee in the above numbered patent was erroneously written and printed as "Negretli" whereas said name should have been written and printed as "Negretti", as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 29th day of August, A. D. 1933.

M. J. Moore.

(Seal) Acting Commissioner of Patents. 

